234 Professor Powell pti ifie Influence of Colour on Heat. 



the publication of my experiments ; whereas, if those experi- 

 ments are worth any thing, his theorij is entirely overthrown, 

 while his experiments are verified, but explained on another 

 principle. Yet it is remarkable how little some of the few 

 authors who have alluded to my researches seem to have ap- 

 prehended this. And so long as this branch of science con- 

 tinues as it were disowned, equally by all the departments with 

 which it stands more or less connected, and elementary writers 

 are content to copy one from the other, without anv, or only the 

 most superficial examination, it is not surprising that the most 

 erroneous notions should obtain currency, and this in a tenfold 

 degree when the sanction of any great name has unfortunately 

 once been extended to a mistaken view of any point. I cannot 

 forbear referring to the striking instance of this afforded by the 

 misstatement of my experiments given in Dr Thomson's work 

 on Heat, which I endeavoured to correct in a paper in the 

 Annals of Philosophy, November 1830. I am not aware 

 whether, since that time, any amended edition has appeared ; 

 but certainly, views of the subject scarcely less vague and mis- 

 conceived, (as appears to me), have emanated from several quar- 

 ters from whence their appearance has greatly surprised me. 



Having deviated a little from the precise line which 1 had 

 proposed to follow in this communication, I may perhaps be ex- 

 cused in diverging a little further, to introduce another remark 

 connected with the same subject, which is hardly worthy of a 

 distinct paper, and which may tend to render the present argu- 

 ment more complete to those readers who may not have the in- 

 chnation or opportunity to seek further for elucidation of my 

 views. I refer more particularly to the inferences made from 

 De la Roche's experiments, and my explanation of his results, 

 though denying that inference. 



The results I allude to, and the inferences from them, are as 

 follows. 



When the hot body was wori-luminous, the effect when a 

 plain glass was interposed was greater than with a blackened 

 glass ; but since the transmission of heat by absorption and sub- 

 sequent radiation must have been at least equal in the latter case 

 to that in the former, and most probably greater, the effect 



